In 1851 the astronomer Jean Bernard Leon Foucault, while working on
a conical pendulum clock to regulate a telescope drive, realized that with
an ideal pendulum
supported at the north pole "the motion of the earth, which forever
rotates from west to east, will become appreciable in contrast with the
fixity of the plane of
oscillation". Although he further wrote that "when our latitudes are
approached, the phenomenon becomes complicated in a way that is rather
difficult to appreciate",
he did intuit that the effect would be proportional to the sine of
the latitude. His first experiments were with a 2 m pendulum in his basement
but he quickly went on to
construct a 67 m pendulum at the Pantheon in Paris. This pendulum created
a sensation at the Paris exhibition in 1851 and generated both a flood
of experiments
around the world and an enormous scientific literature. In the autumn
of 1995, the 28 kgm iron sphere used by Foucault was dusted off and again
rehung from the
Pantheon dome as in 1851.
In describing his experiments in 1851 Foucault noted he was aware of
a 1837 paper on the deviation of projectiles in which Poisson used the
calculations of his
student Coriolis from 1831 on accelerations in rotating frames of reference.
Poisson thought the effect unobservable but Foucault clearly understood
that "a
pendulum has the advantage of accumulating the effects". The experiment
was crucial to the development of mechanics; it established the force concept
of Coriolis as useful and the subsequent work cleared up misconceptions
people had on the effect of the rotation of the earth on air flow in the
atmosphere.